The present invention relates to a projection type liquid crystal display device or more specifically to a projection type liquid crystal display device which projects and visualizes on a screen an image displayed by a liquid crystal display element.
FIG. 4 is a block diagram showing the construction of the conventional liquid crystal display device 1 which comprises a projector 2 and a screen 11. In the projector 2, light L from a light source 3 is directed by a reflection mirror 10 in the forward direction (in the leftward direction of FIG. 4) and collected by a condenser lens 4. The condensed light L passes through a heat absorbing filter 5 where heat is eliminated. Then the light is linearly polarized by a primary polarizing plate 6. The linearly polarized light then passes through a liquid crystal display element 7 where the polarized light is subjected to the optical rotatory modulation according to an image to be displayed. Then the light passes through a secondary polarizing plate 8 which transforms the light into a pattern of luminance in accordance with the image to be displayed. The pattern is enlarged by a projection lens 9 and projected on the external screen 11 located in the left of FIG. 4.
The screen 11 comprises a sheet material 12 and a reflection sheet 13 covering the surface of the sheet material 12. An image projected by the projector 2 onto the screen 11 is reflected by the reflection sheet 13 so that a viewer can see the image from the arrow direction X.
The above conventional projection type liquid crystal display device 1 can produce a picture of a high contrast on the screen 11 when no ambient light is incident on the screen 11, as for, in example, a darkroom. When it is light the room, however, the contrast of the picture on the screen 11 degrades severely, influenced by the ambient light incident on the screen 11, making the picture on the screen 11 difficult to see.
When the projection type liquid crystal display device 1 has a color display function, the influence of the ambient light is particularly prominent; R (red), G(green) and B(blue) mosaic color filters arranged in parallel corresponding to the display picture elements reduce the intensity of the transmitted light substantially.